To solve a lock inversion problem, we implement part of therange_cyclic algorithm in ext4_da_writepages(). (See commit 2acf2c26for more details.)

As part of that change wbc->range_start was modified by ext4'swritepages function, which causes its callers to get confused sincethey aren't expecting the filesystem to modify it. The simplest fixis to save and restore wbc->range_start in ext4_da_writepages.